Face cam and double follower



Feb. 3, 1959 J. A. 'SHEPHARD 2,871,723

FACE CAM AND DOUBLE FOLLOWER Filed Nov. 18, 1957 2 Sheets-Sheet 1 JAMES A. SHEPHARD ATTORNEY INVENTOR Feb. 3, 1959 J. A. SHEPHARD 2,871,723

FACE CAM AND DOUBLE FOLLOWER Filed Nov. 18, 1957 v 2 Sheets-Sheet 2 ATTORNEY United States Patent FACE CAM AND DOUBLE FOLLOWER James A. 'Shephard, St. Petershurg, Fla., assiguor to Universal Winding Company, Cranston, R. L, a corporation of Massachusetts Application November 18, 1957, Serial No. 697,097

Claims. (Cl. 74-567) This application relates to the art of mechanical movements and is concerned more particularly with a cam and follower arrangement for converting rotary to linear motion.

It is common practice in this art to drive a reciprocating member by a so-called constant diameter plate cam, the opposite edges of which are engaged by opposed followers carried on the member to be driven. In this arrangement, the maximum throw, or extent of linear movement, that can be imparted to the reciprocatable member is the difference between the maximum and minimum radii of the plate cam.

Therefore, the greatest throw that could be theoretically expected would be equal to the maximum radius of the cam; however, since a minimum radius of zero is virtually impossible as a practical matter, the actual throw must be something less than this theoretical maximum.

It is the principal object of the present invention to provide a cam and follower arrangement whichis capable of developing a greater throw than that possible with a plate cam occupying essentially the same amount of space.

A further object of the invention is the provision of a face cam of relatively simple design cooperating with a pair of fixedly spaced, opposed followers which is adapted to move the followers along a linear path a substantially greater extent than a plate cam having the same cam path.

Another object of the invention is the provision of a face cam for imparting reciprocating movement to two fixedly spaced, opposed followers, the cam being formed of a disc mounted for rotation about an eccentric axis'and having a circuitous groove or channel in-the face thereof along which the followers travelone at a time, the maximurndimension-of the groove being inexcess of the fixed distance between the centers of the followers, and also having a recess or pocket extending inwardly from the inner wall of the groove and opening into the groove, which recess receives one follower in essentially inoperative position whilethe' other is traveling in the groove.

Other objects and advantages of the present invention will be apparent from a consideration of the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings, in which:

Figure l is a plan view of a fragment of a mechanism embodying the cam and follower arrangement of the invention;

Figure 2 is a plan view of the cam embodyinga preferred design with the followers being shown in section, the mounting for the followers being omitted to reveal the details of the cam;

Figure 3 is a sectionthrou-gh the cam essentially along line 3-3 of Figure 2, showing the connection of the cam to a drive shaft and the mounting of the followers;

Figure 4 is a planview showingfin solid lines the relative position of the cam and followers when the former is rotated 90 9 fromthe position? of Figure 2 and in dotted 2,871,723 liatented Feb. 3, 1959 lines the relative position upon a further 45 rotation; and

Figure 5 is a plan view showing in solid lines the relative position of the cam and followers when rotated from the position of Figure 2, the position of Figure 2. being included in dotted lines for sake of comparison.

Referring now to Figures 2 and 3, in particular, the numeral 11) designates a plate or disc of wear resistant metal or the like which is mounted eccentrically upon a shaft for rotation therewith. To this end, an aperture 12 may be formed in the disc at a point offset from the center thereof and the reduced end portion 14 of a shaft 16 in= serted therein. The shaft may be rotated by a gear 18, only a fragment of which is shown, having its upper face abutting the under face of the disc 10, gear 18 being secured to the disc by a locking screw 20 in order that the two rotate as a unit. Gear 18 is provided with a hub or boss 22 through which extends a bore 23 equal in diameter to aperture 12 and coaxial therewith and reduced portion 14' of shaft 16 is press-fitted into this bore. Shoulder 15 determines the extent to which portion 14 penetrates into the disc.

For purposes of illustration, the cam selected provides a curve or path of modified heart shape, which is to say that the cam path is a single lobe with its sides defined by symmetrical generally involute-shaped curves. In Figure 2, the cam curve is indicated by the dash-dot line 24-. It will be notedghowever, that the cam curve 24 differs from the ordinary involute curve in that the two symmetrical halves intersect with one another at the axis 25 of shaft 16 and extend generally radially inwardly from this point ofintersection along a flat are to a common inner end point 26 spaced'inw'ardly from the initial point of intersection25'in the direction of the axis of disc 10 along a straight line passingthrough the axis of' shaft 16 and the axis of the disc. From the point 25, the two halves extend outwardly, around, and then'inwardlyalong ever increasing radii (much as the usual involute curve) to a common outer end point 27 which forms the apex of the salient angle of the cam curves More specifically, the cam curve, as a whole, is in substantially the shape of a curtate cardioid.

Asthe cam in-questionis of the face type, the cam'curve is defined orestablished bya groove cut into the faceof disc 1-0, which groove is identified herein by numeral 28, and having an inner wall-23a and an outer wall 28b separated by a-fixed distance throughout their length. From the apex 27 of the cam curve, groove'28 extends along a major portion of the length of both the upper and lower halves of cam curve 24. As the reentrantangle, i. e., point 25, is approached, the groove stops as suchand opens into an enlarged pocket or recess 29- extending inwardly toward the center of disc 10 and defined in the embodiment of Figure 2 by a U-shaped wall 30 which joins the inner wall- 28:! of groove 28 at the terminations thereof on either-side ofpoint 25. In-other words, in the canrof the invention, there is no clearlydefined reentrant angle; rather, the reentrant angle, or more properly, the curtate portion of the cam curve, is replacedor absorbed by a cut-out of larger dimensionsin-the face of the cam, this being made possible by the elimination of the reentrant angle asa necessary element of the earn, as will be more clearly explained'later.

As can be. best seen in Figure 3, there is associated with the disc ltla pair of camfollowers 31a and 315 which are held in fixed spaced relationship by a follower block 32. By means not shown'in'Figure 3, the follower block is constrained 7 to move along-a straight line passing through the axisofshaft 16' (point 25) and is connected in any desired manner to'a connecting rod (not shown) which moves the instrumentality robe actuated by. the

cam.

The relative movement of the cam and followers is shown in Figures 4 and 5 along with Figure 2. Assuming that the cam and followers are initially in the position of Figure 2, follower 31b is'at the apex27 of the cam curve 24 while follower 31a is within the recess 29 with its axis resting on the common inner end point of the two curve halves. As .the disc is rotated 90 about the axis of shaft 16 in a counterclockwise direction to the solid line position of Figure 4, follower 31b is shifted towards the left in Figure 2 by the outer wall of one half of groove 24 along a straight line passing through the follower axes and the axis of rotation of the disc (point 25) toward the latter axis while follower 31b moves within recess 29 along a diametrically reverse path. In the 90 position, follower 31b is just about to emerge from one end of the groove 28 into the enlarged recess 29 in the cam face while follower 31a has just entered the other end of groove 28 from recess 29. As rotation is continued for another 45 to the dotted line position in Figure 4, follower 31a is urged by the inner wall of the other half of groove 28 towards the left in Figure 4 away from the axis of rotation of the cam disc while follower 31b is following a diametrically reverse path in recess 28 until its axis coincides with point 25. In the solid line position of Figure 5, after a total of 180 rotation, follower 31:: will have reached the apex 27 of the salient angle of the cam path while follower 3% will have reached the common inner end point of the cam curve in recess 29. Now, the position of the followers is exactly reversed from their initial position and it will be understood that the movement of the followers throughout the remaining 180 of rotation will be just the opposite from that described above.

It will be understood from the foregoing description that certain conditions must be maintained in the relationship of the cam surfaces, i. e., groove walls, and the followers. First, the wall 30 of recess 29 must be spaced from the inner wall of the groove 28 along all of the possible straight lines passing through the axis of rotation and intersecting the lines of the walls a distance equal or less than the distance separating the cam followers at their closest or innermost points. The followers are spaced apart a fixed distance and obviously could not be separated by a solid portion of disc 10 that is longer than this fixed distance. Second, the distance between the two points at which the wall of recess 29 joins the inner wall of groove 28 cannot exceed the distance separating the axes of the two followers and is preferably somewhat less than this distance. One follower must enter the recess as the other leaves and it must not be possible for both to be received in the recess at the same time. Third, the ingress and egress ends of groove 28, that is, the mounts of the groove adjacent either side of recess 29 must be substantially symmetrical with respect to the centerline of the cam. The followers are separated by a fixed distance, move along a straight line and one takes over control as the other releases it. Preferably, the entire cam is symmetrical but this does not appear essential so long as one follower is entering the groove in exactly the reverse motion of the other follower as it leaves the groove, ,provided, of course, that the curvature of the remainder of the groove satisfies the first condition enumerated above.

Each of the followers is in control, so to speak, over a period of 180 of rotation of disc 10 while the other is inactive over the same period. Thus, in the arrangement of the drawings, follower 31a is active from about the 90 to the 270 position while follower 31b is active from the 270 position back to the 90 position. Obviously, the curvature of the groove 28 must be so designed that only about 180 of rotation are required for a follower to travel completely from the ingress to the egress end. Subject to this and the other limitations already stated, the curvature is subject to some variation 4 to provide the particular type of motion and acceleration that is desired.

As the follower that is in the recess 29 is constrained to move only along a straight line, side to side movement being prevented, and is moved under the control of the active follower, being incapable of movement except as the other follower moves, the outer wall of the recess 29 may be eliminated, as at 33, although it could just as well be present so long as it clears the path of the followers. By removing it, however, the milling of recess 29 and groove 28 will ofttimes be facilitated. It is desirable that the outer wall of groove 28 at both ends thereof extend inwardly towards the centerline of the cam from points tangential with the followers a short distance when the followers are in the groove entering and leaving positions indicated in solid lines in Figure 4 in order to ensure that the entering follower is effectively within the groove before the other follower actually leaves the other end of the groove.

The increased extent of reciprocation provided by the cam described herein will be apparent from a consideration of Figure 2. A plate cam having an outline such as to afford a cam path similar to path 24 would give a throw equal to the distance between points 25 and 27, overlooking the thickness of the followers and assuming that a plate cam could be designed with its axis of rotation coincident with the reentrant point 25. Moreover, this throw would be decreased to the extent that the axis of rotation is spaced inward from reentrant point 25. In comparison, the throw of the cam of the invention exceeds the maximum possible throw of the corre sponding plate cam by the distance between points 25 and 26. This throw can be increased by designing the cam such as to move the end point 26 still farther inwardly from point 25.

In Figure 1, the cam and follower arrangement is shown in operative association with a proportioning mechanism and a member to be actuated. The numeral 40 indicates a frame having bearings 42 at opposite sides in which a rod 44 is freely received for reciprocating movement. Rod 44 is connected at the end not shown to any suitable device to be driven. Within the frame, and above disc 10, is a circular disc 46 having its center in axial alignment with the axis of rotation of said disc and which may be rotated to any desired position and retained thereat. An elongated rectangular track 48 extends diametrically across disc 46 in which track follower plate 32 is adapted to move. Follower plate 32 carries an upstanding pin 50 which fits for free sliding movement in an elongated slot 52 formed in the underside of a cross-head 54 at right-angles to the axis of rod 44. To connect the crosshead to rod- 44, the former is provided with a boss 56 which is bored for the introduction of the rod, set screw 58 serving to prevent independent movement of the rod. By rotating disc 46 from a position at which track 48 is at right-angles to rod 44 to a position at which the track is aligned with rod 44, the reciprocating motion of rod 44 may be varied from 0 to of the maximum throw afforded by the cam.

It hardly need be said that the invention will find utility in numerous applications, among the foremost of which is as a part of a coil-Winding machine. When so employed, the rod 44 will carry a guide for the strand being wound so that the strand will be traversed as the rod is reciprocated.

Certain modifications and alterations in the design of the components of the invention specifically illustrated and described have already been alluded to and others will be apparent to one skilled in the art. For this reason, the scope of the invention is not determined by the illustrative embodiment but rather by the hereunto appended claims.

Having thus described the invention, that which is claimed is:

1. The combination with a pair of followers mounted in fixed spaced relationship for reciprocating movement, of a face cam comprising a plate rotatable about an axis lying on the line of reciprocation of the followers and disposed eccentrically relative to the plate center, a circuitous groove in the face of said disc in which said followers are adapted to travel and having a maximum dimension in excess of the distance between the follower axes, an enlargement in said groove extending inwardly from the inner edge thereof in the direction of the maximum projection of said groove from said axis of rotation, the wall of said enlargement being spaced from the inner wall of the groove along radii through the axis of rotation a distance less than the distance between the followers at their closest points, the edges of the enlargement wall at their juncture with the inner wall of the remainder of the groove being spaced apart a distance less than the distance between the centers of said followers whereby said followers alternately travel in said groove and remain in said enlargement upon rotation of the disc.

2. The combination with a pair of followers mounted in fixed spaced relationship for reciprocating movement, of a face cam rotatable about an eccentric axis and adapted to provide a continuous cam path-having an outer and an inner loop, said followers alternating from one loop to the other, said cam comprising a plate having a circuitous groove in the face defining the major portion of the outer loop of the path and a pocket of the same depth as said groove in the face of the plate and extending inwardly of said groove, said pocket being of greater dimensions than the inner loop of the path and encompassing the same, the followers being received, one at a time, in said pocket while moving through the inner loop of the path, one follower entering said pocket from the groove as the other leaves the pocket and enters the groove.

3. The combination with a pair of followers mounted in fixed spaced relationship for reciprocating movement, of a face cam having a path generally in the shape of a symmetrical curtate cardioid, said face cam comprising a plate mounted for rotation about an eccentric axis, a groove in the face of said plate having two symmetrical arcuate halves joined at one end and diverging from said end in approximately V-shape, and a generally U-shaped pocket in said plate connecting the other ends of the halves of said groove and extending inwardly therefrom, said pocket being defined by a bottom wall coplanar with the floor of said groove and an end wall, said end wall being separated from the inner wall of the groove at points lying on straight lines radiating frorn the axis of rotation of the plate a distance not greater than the minimum distance between said followers, the ends of said groove halves connected by said pocket being spaced apart not more than the distance between the follower axes, said followers being alternately received by said groove and pocket as said plate rotates.

4. The combination of claim 3 wherein said axis of rotation of the plate lies on the axis of symmetry of the cam path and on the cam path as well.

5. The combination of claim 3 wherein said groove receives one of said followers and the pocket the other of said followers through the first of rotation of the plate and the followers are reversed in position during the remaining 180 of rotation.

References Cited in the file of this patent UNITED STATES PATENTS I 629,039 Luitwieler et a1 July 18, 1899 1,379,846 Benson May 31, 1921 2,566,034 Roberts Aug. 28, 1951 FOREIGN PATENTS 401,263 France Aug. 24, 1909 

